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Three series of poly(pyromellitimide-ester)s were synthesized from various N, NЈ-bis(-hydroxyalkyl)pyromellitimides (HAPMIs) by melt condensation with dicarboxylic acids, including terephthalic acid (TPA), 4,4Ј-biphenyldicarboxylic acid (BPDA), and 4,4Ј-azobenzenedicarboxylic acid (ABDA). Polymers were characterized by elemental analysis, solubility, inherent viscosity, spectra (IR, 1 H-NMR, 13C-NMR), and X-ray diffraction (XRD). Thermal stability and phase transition behaviour were evaluated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and hotstage optical polarized microscopy (HOPM). The d-spacings, calculated from XRD data, showed an odd-even effect with varying numbers of methylene spacers. Crystallinity of polymers decreased in the following order: azobenzene Ͼ biphenyl Ͼ phenyl polymers. Similarly, DSC-obtained melting temperatures (T m 's) showed an odd-even effect, and glass transition temperatures (T g 's) decreased with increasing numbers of methylene spacers. Thermal stability decreased as methylene chain length increased. Thermal stability of polymers occurred in the following order: phenyl Ͼ biphenyl Ͼ azobenzene polymers.

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